Title page for ETD etd-07132007-075601

Type of Document Master's Thesis
Author Li, Yan
Author's Email Address yli13@lsu.edu
URN etd-07132007-075601
Title Denitrification Capacity and Denitrifying Bacteria in a Restored Bottomland Hardwood Forest, Mississippi River Alluvial Valley: Hydrological Impacts
Degree Master of Science (M.S.)
Department Environmental Studies
Advisory Committee
Advisor Name Title
Aixin Hou Committee Chair
Stephen P. Faulkner Committee Member
Vincent L. Wilson Committee Member
Walter R. Keithly Committee Member
  • restoration
Date of Defense 2007-06-29
Availability unrestricted
Mississippi River Alluvial Valley (MAV) is one of the most important ecosystems in the United States, and bottomland hardwood forests (BLHs) are a major components of this ecosystem. The ecological and hydrological functions of BLHs can help maintain the diversity of species, groundwater balance, and nutrient removal etc. However, due to the increased human activities in the area, most of the BLHs were converted to agricultural land. Realizing the seriousness of the situation of the ecosystem, a series of programs have been carried out by the U.S. Fish and Wildlife Service (USFWS) and the U.S. Department of Agriculture (USDA) to restore the forested wetlands since several decades ago. However, the efficacy of these activities on denitrification is unclear. In this study, field and laboratory studies were carried out to determine the effects of hydrologic restoration (i.e. periodical flooding) on the denitrification capacity and denitrifying bacteria in a 30-year old restored BLH in the Red River Wildlife Management Area (RAWMA) of the MAV, and designed a better cultivation medium for denitrifying bacteria isolation from soils in this area. In-situ denitrification was estimated using the C2H2 block technique with a static chamber and potential denitrification rate was determined in the laboratory using a modification of the denitrification enzyme assay (DEA) method. Both in-situ and potential denitrification rates with amendment of nitrate (NO3-) were significantly (P < 0.05) higher at flooded, lower elevation sites than those of higher elevation sites where the hydrology was not restored. Without amendment of NO3-, no significant differences in potential and in situ denitrification rates were observed between low and high elevations. The population of denitrifying bacteria was measured by the most probable number (MPN) method, and denitrification gene nirK quantified by real-time quantitative PCR. The MPN and PCR results were consistent with each other, without significant differences between the high and low elevation sites. The isolation rates of denitrifying bacteria from the designed medium No. 1 and No. 2 were higher than the classic cultivation medium. The numbers of species isolated by these two media still need to be determined, and compared to the classic one. Further improvement of the medium will be based on the evaluation of this first generation of media.
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